1. Field of the Invention
The present invention relates generally to an ignition time controller, an ignition time control method and engine control unit for an internal combustion engine, and more particularly, to an ignition time controller, an ignition time control method and an engine control unit for an internal combustion engine which has a cam phase changing mechanism for changing the cam phase of at least one of an intake cam for opening/closing an intake valve and an exhaust cam for opening/closing an exhaust valve to reach a target cam phase so that the engine is operated in a combustion mode switched between a uniform combustion mode which performs fuel injection during an intake stroke and a stratified combustion mode which performs fuel injection in a compression stroke.
2. Description of the Prior Art
A conventional ignition time controller for an internal combustion engine of the type mentioned above is known, for example, from Laid-open Japanese Patent Application No. 9-209895. An internal combustion engine described in this document comprises a cam phase changing mechanism which changes the phase of an intake cam (hereinafter referred to as the xe2x80x9ccam phasexe2x80x9d) with respect to a crank shaft. The cam phase is controlled to reach a target cam phase, as a target value, to change a valve timing of an intake valve, i.e., overlapping of the intake valve with an exhaust valve, and so on, thereby controlling the intake characteristics represented by a filling efficiency, and internal EGR. The target cam phase is determined based on the engine rotational speed and a load (an intake air mass per rotation of the engine). Also, this controller determines a basic ignition time based on the engine rotational speed and load, calculates a cam phase deviation which indicates the amount of deviation of an actual cam phase from the target cam phase, and determines a correcting amount for the basic ignition time based on the engine rotational speed, load and cam phase deviation.
Also, a recent internal engine, known as a direct injection type, directly injects a fuel into a cylinder, and is operated in a combustion mode which is switched between a uniform combustion mode and a stratified combustion mode in order to improve the fuel economy (see, for example, Laid-open Japanese Patent Application No. 11-22508). In this internal combustion engine, the stratified combustion mode is performed during an extremely low load operation such as idling, wherein a fuel injection is performed during an intake stroke with a throttle valve being substantially fully opened to supply a large amount of intake air into a cylinder for burning at an extremely leaner air/fuel ratio than the stoichiometric air/fuel ratio. On the other hand, the uniform combustion mode is performed during operations other than the extreme low load operation, wherein a fuel injection is performed during a compression stroke, and a throttle valve opening is controlled in accordance with the engine rotational speed and load to control the amount of intake air for burning at a richer air/fuel ratio than in the stratified combustion mode.
As described above, the conventional ignition time controller employs the intake air mass per rotation of engine as representative of the load which is relied on as a parameter to determine a basic ignition time. On the other hand, the load varies as the actual cam phase of the cam phase changing mechanism varies to cause a change in the filling efficiency, amount of intake air, and so on. As a result, this ignition time controller suffers from a delay in convergence of the ignition time to an optimal value due to the continuously fluctuating basic ignition time resulting from the varying actual cam phase, and therefore encounters difficulties in setting at all times an optimal ignition time in accordance with an engine operating condition.
This problem is particularly prominent when the ignition time controller is employed in the aforementioned direct injection type internal combustion engine, and particularly, when the engine is operated in the stratified combustion mode. Specifically, as described above, since the combustion is performed in an extremely lean air/fuel ratio in the stratified combustion mode, the fuel is inherently more difficult to burn in the stratified combustion mode than the uniform combustion mode. For this reason, if the ignition time delays in convergence to an optimal value, particularly, in the stratified combustion mode, the combustion state is more likely to deteriorate, thereby resulting in lower operability and exhaust gas characteristics.
The present invention has been made to solve the problem as mentioned above, and its object is to provide an ignition time controller, an ignition time control method and an engine control unit for an internal combustion engine which are capable of setting an ignition time to an optimal value in accordance with a change in intake characteristics associated with a change in cam phase such that the ignition time rapidly converges to the optimal value in either of the uniform combustion mode and the stratified combustion mode in a direct injection type internal combustion engine having a cam phase changing mechanism.
To achieve the above object, according to a first aspect of the present invention, there is provided an ignition time controller for an internal combustion engine equipped with a cam phase changing mechanism for changing a cam phase with respect to a crank shaft for at least one of an intake cam for opening/closing an intake valve and an exhaust cam for opening/closing an exhaust valve such that the cam phase reaches a target cam phase, so that the engine is operated in a combustion mode switched between a uniform combustion mode in which a fuel is injected into a cylinder during an intake stroke and a stratified combustion mode in which a fuel is injected into a cylinder in a compression stroke.
The ignition time controller according to the first aspect of the present invention is characterized by comprising engine rotational speed detecting means for detecting a rotational speed of the internal combustion engine; accelerator pedal opening detecting means for detecting an opening of an accelerator pedal; required torque determining means for determining a required torque outputted by the internal combustion engine based on the detected engine rotational speed and accelerator pedal opening; fuel injection time determining means for determining a time at which a fuel is injected into the cylinder; basic ignition time determining means for determining a basic ignition time based on the engine rotational speed and the determined required torque when the engine is in the uniform combustion mode, and for determining the basic ignition time based on the engine rotational speed and the determined fuel injection time when the engine is in the stratified combustion mode; actual cam phase detecting means for detecting an actual cam phase; and ignition time correcting means for correcting the basic ignition time in accordance with a cam phase deviation which is a difference between the detected actual cam phase and the target cam phase.
The internal combustion engine is operated in a combustion mode switched between the uniform combustion mode in which a fuel is injected into a cylinder in an intake stroke and the stratified combustion mode in which the fuel is injected in a compression stroke. Also, according to the ignition time controller in the first aspect of the present invention, the basic ignition time is determined based on the engine rotational speed and required torque in the uniform combustion mode. Since the required torque is determined as a torque outputted by the internal combustion engine based on the engine rotational speed and accelerator opening, the required torque reflects an actual load, and is not affected directly by a change, if any, in the intake characteristics such as a filling efficient associated with a change in cam phase of the cam phase changing mechanism, so that the required torque presents an extremely small amount of fluctuations due to such a change. Therefore, in the uniform combustion mode, the basic ignition time can be appropriately set in accordance with the required torque, i.e., the load, in a stable manner without significantly affected by a change in the intake characteristics associated with a change in the cam phase.
On the other hand, in the stratified combustion mode, the basic ignition time is determined based on the engine rotational speed and the fuel injection time. In the stratified combustion mode, the ignition time must be accurately set in coincidence with a time at which an air/fuel mixture exists near an ignition plug because the fuel is injected in a compression stroke. Thus, the basic ignition time can be appropriately set by determining the same based on an actual fuel injection time. Also, since the fuel injection time is not either affected directly by a change in the intake characteristics associated with a change in the cam phase, the basic ignition time can be stably and appropriately set in the stratified combustion mode.
Also, the basic ignition time determined as described above is corrected in accordance with the cam phase deviation between the actual cam and the target cam, so that an optimal ignition time can be set corresponding to the actual intake characteristics. Thus, according to the ignition time controller of the present invention, the basic ignition time can be stably and appropriately set without significantly affected by a change in the intake characteristics associated with a change in the cam phase, and the basic ignition time is corrected in accordance with the cam phase deviation, thereby making it possible to set the ignition timing such that it rapidly converges to an optimal value in accordance with the change in the intake characteristics associated with the change in the cam phase.
To achieve the above object, according to a second aspect of the present invention, there is provided an ignition time controller for an internal combustion engine equipped with a cam phase changing mechanism for changing a cam phase with respect to a crank shaft for at least one of an intake cam for opening/closing an intake valve and an exhaust cam for opening/closing an exhaust valve such that the cam phase reaches a target cam phase, so that the engine is operated in a combustion mode switched between a uniform combustion mode in which a fuel is injected into a cylinder during an intake stroke and a stratified combustion mode in which a fuel is injected into a cylinder in a compression stroke.
The ignition time controller according to the second aspect of the present invention is characterized by comprising an engine rotational speed detecting module for detecting a rotational speed of the internal combustion engine; an accelerator pedal opening detecting module for detecting an opening of an accelerator pedal; a required torque determining module for determining a required torque outputted by the internal combustion engine based on the detected engine rotational speed and accelerator pedal opening; a fuel injection time determining module for determining a time at which a fuel is injected into the cylinder; a basic ignition time determining module for determining a basic ignition time based on the engine rotational speed and the determined required torque when the engine is in the uniform combustion mode, and for determining the basic ignition time based on the engine rotational speed and the determined fuel injection time when the engine is in the stratified combustion mode; an actual cam phase detecting module for detecting an actual cam phase; and ignition time correcting module for correcting the basic ignition time in accordance with a cam phase deviation which is a difference between the detected actual cam phase and the target cam phase.
This ignition time controller provides the same advantageous effects as described above concerning the ignition time controller according to the firs aspect of the present invention.
To achieve the above object, according to a third aspect of the present invention, there is provided an ignition time control method for an internal combustion engine equipped with a cam phase changing mechanism for changing a cam phase with respect to a crank shaft for at least one of an intake cam for opening/closing an intake valve and an exhaust cam for opening/closing an exhaust valve such that the cam phase reaches a target cam phase so that the engine is operated in a combustion mode switched between a uniform combustion mode in which a fuel is injected into a cylinder during an intake stroke and a stratified combustion mode in which a fuel is injected into a cylinder in a compression stroke.
The ignition time control method according to the third aspect of the present invention is characterized by comprising the steps of detecting a rotational speed of the internal combustion engine; detecting an opening of an accelerator pedal; determining a required torque outputted by the internal combustion engine based on the detected engine rotational speed and accelerator pedal opening; determining a time at which a fuel is injected into the cylinder; determining a basic ignition time based on the engine rotational speed and the determined required torque when the engine is in the uniform combustion mode, and determining the basic ignition time based on the engine rotational speed and the determined fuel injection time when the engine is in the stratified combustion mode; detecting an actual cam phase; and correcting the basic ignition time in accordance with a cam phase deviation which is a difference between the detected actual cam phase and the target cam phase.
This control method provides the same advantageous effects as described above concerning the ignition time controller according to the firs aspect of the present invention.
To achieve the above object, according to a fourth aspect of the present invention, there is provided an engine control unit including a control program for causing a computer to carry out ignition time control for an internal combustion engine equipped with a cam phase changing mechanism for changing a cam phase with respect to a crank shaft for at least one of an intake cam for opening/closing an intake valve and an exhaust cam for opening/closing an exhaust valve such that the cam phase reaches a target cam phase so that the engine is operated in a combustion mode switched between a uniform combustion mode in which a fuel is injected into a cylinder during an intake stroke and a stratified combustion mode in which a fuel is injected into a cylinder in a compression stroke.
The engine control unit according to the fourth aspect of the present invention is characterized in that the control program causes the computer to detect a rotational speed of the internal combustion engine; detect an opening of an accelerator pedal; determine a required torque outputted by the internal combustion engine based on the detected engine rotational speed and accelerator pedal opening; determine a time at which a fuel is injected into the cylinder; determine a basic ignition time based on the engine rotational speed and the determined required torque when the engine is in the uniform combustion mode, and determining the basic ignition time based on the engine rotational speed and the determined fuel injection time when the engine is in the stratified combustion mode; detect an actual cam phase; and correct the basic ignition time in accordance with a cam phase deviation which is a difference between the detected actual cam phase and the target cam phase.
This engine control unit provides the same advantageous effects as described above concerning the ignition time controller according to the firs aspect of the present invention.
Preferably, in the ignition time controller, the basic ignition time correcting means includes advance direction correcting means for correcting the basic ignition time in an advance direction when the cam phase deviation is larger than an upper limit predetermined value.
With this configuration, the basic ignition time is corrected in the advance direction when the cam phase deviation is larger than the upper limit predetermined value, i.e., when the actual cam phase deviates in the advance direction with respect to the target cam phase, so that the ignition time can be more appropriately set corresponding to the direction of actual deviation of the cam phase. Also, since the basic ignition time is corrected only when the cam phase difference is larger than the upper limit predetermined value, i.e., when the amount of actual deviation of the cam phase is large, the stability of the ignition time can be maintained.
Also, preferably, in the ignition time controller, the basic ignition time correcting module includes an advance direction correcting module for correcting the basic ignition time in an advance direction when the cam phase deviation is larger than an upper limit predetermined value.
This preferred embodiment of the ignition time controller provides the same advantageous effects as provided by the corresponding preferred embodiment of the ignition time controller.
Also, preferably, in the ignition time control method, the step of correcting the basic ignition time includes correcting the basic ignition time in an advance direction when the cam phase deviation is larger than an upper limit predetermined value.
This preferred embodiment of the control method provides the same advantageous effects as provided by the corresponding preferred embodiment of the ignition time controller.
Also, preferably, in the engine control unit, when the control program causes the computer to correct the basic ignition time, the control program causes the computer to correct the basic ignition time in an advance direction when the cam phase deviation is larger than an upper limit predetermined value.
This preferred embodiment of the engine control unit provides the same advantageous effects as provided by the corresponding preferred embodiment of the ignition time controller.
Also, preferably, in the ignition time controller, the basic ignition time correcting means includes retard direction correcting means for correcting the basic ignition time in a retard direction when the cam phase deviation is smaller than a lower limit predetermined value.
With this configuration, the basic ignition time is corrected in the retard direction when the cam phase deviation is smaller than the lower limit predetermined value, i.e., when the actual cam phase deviates in the retard direction with respect to the target cam phase, so that the ignition time can be more appropriately set corresponding to the direction of actual deviation of the cam phase, and the stability of the ignition time can be maintained, as is the case with the control of the ignition time when the cam phase deviates in the advance direction.
Also, preferably, in the ignition time controller, the basic ignition time correcting module includes a retard direction correcting module for correcting the basic ignition time in a retard direction when the cam phase deviation is smaller than a lower limit predetermined value.
This preferred embodiment of the ignition time controller provides the same advantageous effects as provided by the corresponding preferred embodiment of the ignition time controller.
Also, preferably, in the ignition time control method, the step of correcting the basic ignition time includes correcting the basic ignition time in a retard direction when the cam phase deviation is smaller than a lower limit predetermined value.
This preferred embodiment of the control method provides the same advantageous effects as provided by the corresponding preferred embodiment of the ignition time controller.
Also, preferably, in the engine control unit, when the control program causes the computer to correct the basic ignition time, the control program causes the computer to correct the basic ignition time in a retard direction when the cam phase deviation is smaller than a lower limit predetermined value.
This preferred embodiment of the engine control unit provides the same advantageous effects as provided by the corresponding preferred embodiment of the ignition time controller.
Further, preferably, in the ignition time controller, the basic ignition time correcting means corrects the basic ignition time with different correcting amounts when the engine is in the uniform combustion mode and when the engine is in the stratified combustion mode.
Generally, the ignition time is largely affected by a change in internal EGR amount and effective compression ratio associated with a change in the cam phase in the uniform combustion mode, whereas the ignition time is less affected by the cam phase but rather largely affected by a fuel injection time in the stratified combustion mode. Therefore, according to the present invention, in the uniform combustion mode and the stratified combustion mode, the basic ignition time is corrected using a correcting amount adapted to the characteristics of the respective modes, so that the ignition time can be more appropriately set.
Further, preferably, in the ignition time controller, the basic ignition time correcting module corrects the basic ignition time with different correcting amounts when the engine is in the uniform combustion mode and when the engine is in the stratified combustion mode.
This preferred embodiment of the ignition time controller provides the same advantageous effects as provided by the corresponding preferred embodiment of the ignition time controller.
Further, preferably, in the ignition time control method, the step of correcting the basic ignition includes correcting the basic ignition time with different correcting amounts when the engine is in the uniform combustion mode and when the engine is in the stratified combustion mode.
This preferred embodiment of the control method provides the same advantageous effects as provided by the corresponding preferred embodiment of the ignition time controller.
Further, preferably, in the engine control unit, when the control program causes the computer to correct the basic ignition time, the control program causes the computer to correct the basic ignition time with different correcting amounts when the engine is in the uniform combustion mode and when the engine is in the stratified combustion mode.
This preferred embodiment of the engine control unit provides the same advantageous effects as provided by the corresponding preferred embodiment of the ignition time controller.
Furthermore, the engine includes a fuel injection valve for injecting the fuel which is disposed in a central portion of a top wall of a combustion chamber of the cylinder for injecting the fuel toward a recess formed in a piston.
According to this preferred embodiment, the advantageous effects provided by the ignition time controller and the ignition time control method according to the first and second embodiments of the invention and their preferred embodiments described above can be obtained in an optimized manner.
The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.